1. Field of the Invention
The invention is generally related to the area of optical devices. In particular, the present invention is related to optical wavelength multiplexing/demultiplexer or add/drop devices with new optical layouts and manufacturing processes.
2. The Background of Related Art
Optical add/drop and multiplexer/demultiplexer devices are optical components often used in optical systems and networks. These devices using wavelength division multiplexing (WDM) techniques allow a simultaneous transfer of optical signals at different wavelengths or channels through a single optical link such as an optical fiber. In operation, a WDM device or system may need to drop or add a set of channels from or to a transmitting signal. Multiplexer/demultiplexer (Mux/Demux) is often needed for this application.
FIG. 1 replicates a WDM device disclosed in U.S. Pat. No. 5,583,683. A multiple wavelength light beam traveling in a fiber is separated into multiple narrow spectral bands, each directed to an individual port. At each of the ports for a channel, a dielectric thin film filter is used to transmit a specified wavelength in the multi-wavelength (collimated) light passed by the port but reflects all other wavelengths. The remaining of the multi-wavelength signal continues to a next channel port, where an in-band signal at a specific wavelength is transmitted and all others are reflected. The remaining of the multi-wavelength signal continues to propagate along an optical path. After multiple bounces, signals at different wavelengths are separated. Compared with a conventional three-port cascading modules, the dimension of the device of FIG. 1 is small in size as fiber routing in the three-port modules are replaced with collimated beams, thus the routing overhead is saved.
It is well known that a fiber is not allowed to bend too small. For example, for the widely used SMF-28e fiber, the minimum bend radius is about 30 mm. When being routed, the fiber roll wastes a specific space, for example, 60 mm in diameter for SMF-28e fiber. Without fiber routing, a WDM device box could be even smaller than a square of 30 mm by 30 mm.
Even so, for the prior art device of FIG. 1, the fiber input/output (I/O) ports are positioned on both sides of a mechanical box. In the process of fiber handling, due to the minimum radius limitation, the space waste could be doubled as shown in FIG. 2A. One of the features, objects and advantages of the current invention as will be described below is to have all the I/O ports deposed on one side of a device as shown in FIG. 2B. For a one-sided device, as the I/O ports are on one side of the device, thus fiber routing could be eliminated.
The one-sided optical layout is realized by beam folding components. Prisms or mirrors are commonly used as beam folding components as shown in FIGS. 3A-3C. These components are all to be used and covered by different embodiments of the present invention.
FIG. 4 replicates an optical device of U.S. Pat. No. 6,847,450 using turning prisms to bend light beams from adding channel collimators vertical to the main plane (beam cascading plane). Compared with the prior art device of FIG. 1, the length of the device of FIG. 4 is reduced by a collimator length, but it is at the cost of the height as the cascading optics is now along with the height dimension of the device of FIG. 4.
FIG. 5 replicates a device of U.S. Pat. No. 7,068,880 that is similar to that of FIG. 4. The major difference is that in U.S. Pat. No. 7,068,880, the beam bending is at the collimator lens while in U.S. Pat. No. 6,847,450 the bending occurs after collimators. In either case, the beams are bent by 90 degrees. The common problem is that the height of the device is now big. As will be described below, the beams are also turned twice to reduce the height of a resulting device. Further unlike these prior art devices, the beam folding occurs along a zigzag optical path, resulting in the height being smaller, compared with prior art devices of FIG. 4 and FIG. 5. As will be appreciated from the disclosure herein, the height of the prior art devices is the width of the zigzagging optics (typically >5 mm) plus two collimator mounting space while the height of a device designed in accordance with the present disclosure is the height of a substrate(typically ˜2 mm) plus two collimator spaces.